This revolutionary discovery could help scientists see black holes for the first time

Of all the bizarre quirks of nature, supermassive black holes are some of the most mysterious because they’re completely invisible.

But that could soon change.

Black holes are deep wells in the fabric of space-time that eternally trap anything that dares too close, and supermassive black holes have the deepest wells of all. These hollows are generated by extremely dense objects thousands to billions of times more massive than our sun.

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CrazyNeutrino said:

This revolutionary discovery could help scientists see black holes for the first time

Of all the bizarre quirks of nature, supermassive black holes are some of the most mysterious because they’re completely invisible.

But that could soon change.

Not SOON change. The article says “Although they don’t emit light, black holes will, under the right conditions, emit large amounts of gravitational waves”. But this happens only when black holes are swallowing large amount of matter – at which times they’re visible anyway in the form of gamma rays and radio waves.

We’re going to have to wait for LISA to observe events like this. The tentative launch date for LISA is 2034. Not what I would call “soon”.

Do black holes have an upper limit on how much mass than can consume or is it nearly infinite

Cymek said:

Do black holes have an upper limit on how much mass than can consume or is it nearly infinite

No, there’s no upper limit. At least, not in standard GR. Quantum gravity theory may impose limits on how small a BH can be, but AFAIK quantum gravity wouldn’t impose an upper limit, so a BH could happily consume the rest of the universe, if you could feed it to the BH, given time. That would be rather difficult to arrange though, due to the universal expansion.

But if there’s a lot of stuff in the vicinity of a BH it can take quite a while for it all to fall in. Actually, some of it won’t fall in. Stuff falling towards a BH picks up a huge amount of speed as it gets close to the hole, approaching c as it gets close to the event horizon, so it has a lot of kinetic energy. And when that stuff collides with other stuff that’s also trying to fall into the BH the results are spectacular. EM radiation right across the spectrum up to high gamma is given off, and matter may ricochet away from the BH’s vicinity.

[FWIW, Hawking radiation theory says that all black holes decay eventually, and the smaller they are the faster they decay. However, stellar and larger sized black holes are currently too cold to decay: their Hawking temperature is colder than the cosmic microwave background, so the CMB heats them up faster than they can decay. So they won’t be decaying until the universe is vastly older & colder than at present.]

We don’t know what happens to matter consumed by black holes do we ?
Could they be like giant capacitors storing all that energy to one day explode releasing it to start another era of star birth

Cymek said:

We don’t know what happens to matter consumed by black holes do we ?
Could they be like giant capacitors storing all that energy to one day explode releasing it to start another era of star birth

black holes slowly release radiation over billions of years

CrazyNeutrino said:

Cymek said:

We don’t know what happens to matter consumed by black holes do we ?
Could they be like giant capacitors storing all that energy to one day explode releasing it to start another era of star birth

black holes slowly release radiation over billions of years

Yes but I wonder if they could release it all at once

Cymek said:

We don’t know what happens to matter consumed by black holes do we ?

No, we don’t. We need a quantum gravity theory to handle questions like that. But even without such a theory its fair to say that normal matter gets ripped apart as it gets close to the centre of a black hole, and that normal matter can’t exist at the very centre, due to the Pauli exclusion principle.

In a pure classical BH, everything falling into a BH ends up in the singularity, which has zero volume, so obviously particles with non-zero volume can’t exist there. But even if quantum effects cause the core of a BH to have non-zero volume it will still be very tiny, far too small to accommodate a star’s worth of fermions (normal matter particles), due to Pauli exclusion. Thus the energy in such a core would have to be in the form of bosons, which aren’t subject to Pauli exclusion, so there’s no limit to the number of bosons that can occupy the same position state.

Fundamental bosons are the particles associated with energy, eg photons. However, you can make composite bosons by binding pairs of fermions together, and it’s possible for large numbers of such composite bosons to share the same position state, but generally such a boson condensate requires very low temperature, and I expect that the extreme gravity near a BH core would rip any composite bosons to pieces. But I’m certainly not an expert on this topic…

Cymek said:

Could they be like giant capacitors storing all that energy to one day explode releasing it to start another era of star birth

Well, if Hawking is correct, all black holes eventually evaporate, and the evaporation rate gets faster & faster as they get smaller. When they’re sufficiently small the evaporation rate becomes explosive. (Quantum gravity may prevent the final phase from being explosive… or it might enhance it).

However, Hawking radiation is primarily in the form of photons, with perhaps a tiny amount of matter – antimatter pairs produced as well. IIRC, the amount of Hawking radiation emitted as matter is probably less than 1 part per billion compared to that released as photons, and that matter would by mostly electrons & positrons, heavier stuff like protons & neutrons would be far rarer. So it’s not the kind of stuff that will lead to new star formation.

OTOH, there’s another possibility that’s probably unlikely, but still rather intriguing. A couple of decades ago, Lee Smolin speculated that the information in a black hole can “give birth” to a new universe that’s otherwise disconnected from the parent universe but which has physical parameters that are fairly similar to that of the parent. This is called the fecund universes theory, aka Cosmological natural selection

small black holes will merge with larger ones

but what happens if two black holes of equal size collide?

If stuff goes into a zero point singularity why are black holes different sizes? Surely that means some have more stuff in them than others?

What is that stuff and how does it relate to the single point thingo?

CrazyNeutrino said:

small black holes will merge with larger ones

but what happens if two black holes of equal size collide?

Sings old song, “two lovely black eyes, two lovely black eyes”, can’t remember the rest, song from the 50’s.

CrazyNeutrino said:

small black holes will merge with larger ones

but what happens if two black holes of equal size collide?

They merge.

AwesomeO said:

If stuff goes into a zero point singularity why are black holes different sizes? Surely that means some have more stuff in them than others?

What is that stuff and how does it relate to the single point thingo?

The usual measure of size of a black hole is the size of its event horizon. The event horizon isn’t a physical object, it’s just a mathematical spherical shell at the distance where the escape speed equals the speed of light. That distance is known as the Schwarzschild radius , and it’s proportional to the mass of the black hole, i.e. if you double the mass of a BH you double its Schwarzschild radius, so it’s a very convenient measure.

When stuff falls into a smallish black hole (one with a mass a few times larger than our Sun’s mass) it will get ripped apart by the tidal force into subatomic particles before it crosses the horizon. But for the big black holes found at galactic cores, stuff can fall across the horizon without even noticing. But as it gets close to the centre it will get ripped apart. As I mentioned earlier, we don’t really know what the end product of this ripping apart process is – our current theories are inadequate to model such extreme conditions. Hopefully, quantum gravity will shed some light on that question.

I guess I ought to mention what that tidal force is. :) Imagine you’re falling feet first into a BH. As you get closer & closer to the core the strength of gravity grows enormously. When you get close enough, the gravity at your feet is much greater than the gravity at your head, so you get stretched. This process is known as spaghettification or the Noodle Effect. :)

Cheers, so there is stuff we just don’t know what it is. So what is the singularity then? And to me a zero point means….ummmm not much. No point? A point so tiny it doesn’t exist?

AwesomeO said:

Cheers, so there is stuff we just don’t know what it is. So what is the singularity then? And to me a zero point means….ummmm not much. No point? A point so tiny it doesn’t exist?

The original Schwarzschild black hole equations say that everything that falls into a BH ends up at a mathematical point in the centre, so using those equations the core of a black hole literally has zero volume. And since density is mass divided by volume, it’d also have infinite density.

However, those original equations are highly idealised, and not expected to perfectly model what a BH in the real world is actually like. In particular, those equations totally ignore quantum theory – any matter falling into the BH is modeled as a mathematical ideal fluid. Also, the original basic Schwarzschild black hole is the sole object in a “toy” universe. It’s eternal – it didn’t form due to gravitational collapse: it was present at the start of the universe, it will exist until the end of the universe, and there’s no other bodies of significant mass in that toy universe.

OTOH, even the Schwarzschild BH is just a toy, it’s a reasonable guide to what a real BH is like. And it’s pretty impressive, considering that it was worked out by a very sick young bloke in the World War One trenches.

Some people use the word “singularity” to refer to whatever is actually in the centre of a real black hole. But others (like me :) ) object to that usage, and prefer to use other terms (eg “core”) since “singularity” (which was borrowed from mathematics) should only be used if the core is actually a zero-volume thingy, which is highly unlikely, but which can’t be ruled out until we get a working theory of quantum gravity.